<html>
<body>
<p><b>Note:</b> This example only works in Firefox and Google Chrome.</p>
<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
<rect x="20" y="20" width="250" height="250" style="fill:blue">
<animate attributetype="CSS" attributename="opacity" from="1" to="0" dur="5s" repeatcount="indefinite"></animate>
</rect>
</svg>
</body>
</html>